idle question

[DopenessFool]

two different idle readings

so i have two different idle readings.
while in park my idle is around 700 to 800 which is right.
but while at a stop light or something it goes down to less than 500 which then causes the car to vibrate.
whats causing this .how do i fixx it?

 

[hgocasca]

Sensors, and you're putting load on the motor when braking, it'll dip a little, but a tune up could help too, either your iac or fitv, try that and report back